Electric smelting furnace of closed-type having dust removing means fixed to exhaust gas vent pipes thereof

ABSTRACT

A closed-type electric furnace to be used for extremely high temperature smelting of a ferroalloy such as metallic silicon or 70 percent ferrosilicon. The furnace has at least two dual service pipes, each of which functions as a raw material charging chute and concurrently as an exhaust gas vent pipe with the aid of its branch pipe, and a plural number of single raw material charging chutes through the furnace lid, whereby each dual service pipe has an automatic dust removing machine at the forked position thereof.

United States Patent 1 Horibe et al.

[541 ELECTRIC SMELTING FURNACE OF CLOSED-TYPE HAVING DUST REMOVING MEANSFIXED T0 EXHAUST GAS VENT PIPES THEREOF [75] Inventors: Koichi Horibe;Tsunenobu Yosida;

Tokuji Machida; Shoji Kaneko; Tomoyuki Sato, all of Arai-shi,Niigata-ken, Japan [73] Assignee: Tanabe Kakoki Co., Ltd., Niigataken,Japan [22] Filed: Apr. 11, 1972 21 Appl. No.: 242,976

[30] Foreign Application Priority Data Apr. 14, 1971 Japan ..46/23566 52US. Cl. ..13/33 51 rm. Cl.

[58] Fieldof Search .L ..13/9,33,

[ 51 June 5,1973

[56] References Cited UNITED STATES PATENTS 3,598,888 8/1971 Tada et al..13/33 3,441,651 4/1969 Viens et al ....l3/9 3,372,223 3/1968 Menegozet al. 1 3/9 Primary Examiner-Roy N. Envall, Jr. Att0rney-So|o'n B.Kemon, Carroll Palmer and William T. Estabrook 57 ABSTRACT A closed-typeelectric furnace to be used for extremely high temperature smelting of aferroalloy such as metallic silicon or 70 percent ferrosilicon. Thefurnace has at least two dual service pipes, each of which functions asa raw material charging chute and concurrently as an exhaust gas ventpipe with the aid of its branch pipe, and a plural number of single rawmaterial charging chutes through the furnace lid, whereby each dualservice pipe has an automatic dust removing machine at the forkedposition thereof.

4 Claims, 6 Drawing Figures PATENTEDJUN Sim SHEET 2 OF 3 I FIG 3 l l I.

FIG-4 ELECTRIC SMELTING FURNACE OF CLOSED-TYPE HAVING DUST REMOVINGMEANS FIXED TO EXHAUST GAS VENT PIPES THEREOF This invention relates toan electric smelting furnace of closed-type, and more particularly tothe one having dust removing means fixed to exhaust gas vent pipesthereof.

Heretofore, electric smelting furnaces of closed-type have been used forthe industrial production of calcium carbide, ferromanganese,ferrochromium, 50% ferrosilicon or other similar substances, thesmelting temperature of these substances being comparatively low. Insmelting of extremely high temperature such as those of metallic siliconor a ferrosilicon containing more than 70 per cent of silicon, there isevolution a large amount of dust evolution mixed with the exhaust gas.Therefore, it has been considered practically impossible to produce suchsubstances using a closed-type smelting furnace, because that thepassage of exhaust gas vent pipe communicated to the furnace lid isliable to be blocked by said largeamount of dust. Unfortunately, thedust of such case has an exceedingly cohesive and solidifying nature,and it is very difficult to remove such coherent dust block from thevent pipe wall.

In a conventional electric smelting furnace of closedtype, the dustaccumulated in the exhaust vent pipe is occasionally cleaned out by aband poking means when the furnace operation is temporarily stopped.However, in the case of aforementioned high temperature smelting,frequent stoppage of its operation would not be permitted because that asmooth and economical production could not be continued.

An object of the present invention is to manufacture a ferroalloynecessitating an extremely high temperature smelting by the use ofclosed-type electric furnace. Another object of the present invention isto provide a closed-type electric furnace suitable for the continuousproduction of 70% ferro'silicon or metallic silicon. These objects maybe attained in accordance with the present invention by setting up aplural number of single raw material charging pipes and at least twodual service pipes having a branched part respectively which function asexhaust gas vent pipes and simultaneously as raw material chargingchutes, whereby each dual pipe has an automatic dust removing machineinstalled at the branched position thereof.

Further objects and advantages of this invention will become apparentwith reference to the following description and the accompanyingdrawings, in which:

FIG. 1 is a longitudinal cross-sectional view, taken along the line AAin FIG. 2, of the upper portion of a preferred embodiment of closed-typeelectric furnace according to the present invention;

FIG. 2 is a cross-sectional plan view of the same taken along the lineB-B in FIG. 1;

FIG. 3 is an enlarged plan view of dust removing machine 10 attached toa dual service pipe 1 in FIG. 1;

FIG. 4 is a longitudinal sectional view of the same taken along the lineD-D in FIG. 3;

FIG. 5 is an enlarged plan view of another dust removing machineattached to a dual service pipe; and FIG. 6 is a longitudinal sectionalview of the same taken along the line E-E in FIG. 5.

In FIGS. 1 and 2, the reference numeral 1 designates a plurality of rawmaterial charging chutes, each of which being designed to serveconcurrently as an exhaust gas vent pipe. This kind of chute pipe willbe referred to in this specification as a dual service pipe hereinafter.The dual pipe 1 has a branch pipe 7 for gas exhaustion at a forkedposition 7a, and is equipped with an automatically acting dust removingmachine 10 at this position.

- As shown in FIG. 2, the number of dual pipe is three in this case. Thefurnace lid 20 is dotted with a plural number of single raw materialcharging chutes therethrough (in FIG. 2, the number thereof beingseven,) near the three electrodes 9 in a usual way. Imaginary linesdesignated by the reference numeral 2 or 3 show examples of the mountingposition and configuration of conventional sole exhaust gas vent. In thepresent invention, however, such conventional mounting positions can notbe adopted by the following reason (1).

As illustrated in FIG. 1, the manners in which the dust may inviteclogging in the electric furnace are roughly classified into thefollowing three types: (1 the dust is accumulated in a peripheral spaceof the furnace lid 20; (2) the dust is deposited on the interior surfaceof each dual service pipe 1 at the lower part thereof, and thedeposition increases in thickness gradually until it invites suchclogging as denoted by the reference numeral 5; and (3) the dust isdeposited at the forked position 7a of each dual service pipe 1 as shownby the reference numeral 6.

In order to avoid the dust clogging indicated by the reference numeral 5in FIG. 1, there may be employed a known method which has been actuallypracticed in some closed-type electric smelting furnace. That is, thelongitudinal interior surface of dual service pipe 1 may be cleaned outwith the charging raw materials la while they fall down through the dualservice pipe 1 intermittently or continuously. The dust particlesdeposited are mostly those of raw materials which have been scattered orevaporated. Therefore, even if they are again thrown into the furnaceaccompanied with new raw materials, there is no harmful effect derivedtherefrom and the'utilization rate of the raw materials is ratherimproved.

Next, an explanation about the prevention of dust ac cumulation 4 at aperipheral space in the'furnace lid 20 of FIG. 1 will be describedhereinafter. In a large scale furnace of closed-type for extremely hightemperature smelting, such as those of metallic silicon or ferrosilicon,a large amount of gas and dust are generated from the surrounding areaof every electrode. Therefore, only one exhaust gas pipe 2 or 3, asshown in FIG. 1, is not suitable for the above-mentioned furnace becausethat the dust accumulation 4 at a part of peripheral space in thefurnace lid 20, which is remote from the sole exhaust gas dust outlet 2or 3, (the relative po sitions of 4 and 2 or 3 is not shown in FIG. 1,)is liable to occur. In the present invention, at least two, preferablythree or more, dual service pipes 1 should be set up through the furnacelid 20 at as near positions as possible to the electrodes 9 as shown inFIGS. 1 and 2. By this means, the dust accumulation at a peripheralspace of furnace lid can be readily ceased to exist.

On the other hand, in case where all of the raw material charging chutesare constructed likewise as the dual service pipe to servesimultaneously as exhaust gas vent pipes, the velocity of gas flowingthrough said pipes would be too low, resulting in that the formationrate of dust clogging at the lower part of each dual service pipe wouldbecome higher than the velocity at which the accumulated dust particlesare all buried into the raw material layer in the furnace. This tends tocause the accumulated dust to block the inlets of the dual servicepipes. Therefore, other than a suitable number, at least two, of dualservice pipes which give a proper velocity to the passing gastherethrough, there must be a plural number, appropriate to that of dualservice pipes, of single raw material charging chutes set up through thefurnace lid.

For removing the dust clog 6 at the forked position 7a of each dualservice pipe 1 in FIG. 1, there must be equipped with an automaticallyacting dust removing machine 10 at said position, and it is operatedcontinuously or intermittently, whereby the dust clog 6 is separatedfrom the branch and is dropped into the inclined,

branch pipe 7 which is a part of vent pipe. Concurrent use of waterflushing into the inclined branch pipe 7, as shown in the later figures,will further increase the dust removing effect like as hitherto. Thedust removing machine 10 according to the present invention permits along-type operation with unchanged performance and safety upon theproduction of metallic silicon or 70% ferrosilicon which accompanies alarge quantity of coagulative dust in the exhaust gas generated by thereductive reaction in the furnace.

Detailed views of the dust removing machine 10 in FIG. 1 are shown inFIGS. 3 and 4. As will be seen, a cleaning piston disc 13 is arranged ina horizontal portion at the juncture of ascending portion 11 of thechute having a water cooling jacket 17 and descending branch pipe 12 ofthe dual service pipe. Said cleaning piston disc 13 is connected to apiston rod 14 of the dust removing machine 16 to make said cleaning disc13 drive reciprocally, and the driving may be performed eithercontinuously or intermittently and automatically by a suitable mechanism(not shown in the figure). The accumulated and coagulated dust on thejuncture part is pushed down into the descending branch pipe 12 by themoving disc 13, and the dust thus swept off is flashed away with waterwhich is injected into the branch pipe 12 from water spray nozzlesaffixed to said branch pipe 12.

FIGS. 5 and 6 show another embodiment of the dust removing machineaccording to the present invention. In this embodiment, a cylindricalrotary disc 24 is disposed on a horizontal juncture end of ascendingchute portion 21 in the top part of descending branch pipe 22 of thedual service pipe, and has a vertical cleaning blade 23 fixed thereto.The cylindrical rotary disc 24 is connected to a motor 27 by means ofgears 26 and a shaft 25 so as to rotate the cleaning blade 23 around thevertical axis of the cylindrical rotary disk 24, whereby the rotation isperformed continuously or intermittently and automatically to sweep offthe deposited dust at the juncture portion. The dust thus swept off isflashed away with water which is injected into the branch pipe 22 fromwater spray nozzles 28 affixed to saidbranch pipe 22.

After several test operations conducted by the usage of 15,000 KVAclosed-type furnace just as shown in FIGS. 1 and 2 for the production ofto ferrosilicon, it was ascertained that continuous and smoothoperations could be carried out successfully for a long time withoutoccurring any accumulation of dust and any clogging or blockage in gaspassages of the furnace.

What we claim is:

1. An improved electric smeltingfurnace of the closed-type whichcomprises a furnace lid, a plurality of single raw material chargingchutes having their discharge end extending through said lid, aplurality of dual service pipes extending at their discharge end throughsaid lid, each of said dual service pipes comprising a raw materialcharging chute and an exhaust gas vent pipe, said chute and vent pipebeing joined at a forked position above said lid and automaticallyoperated means to remove dust from the junction of said chute and ventpipe at said forked position.

2. An improved electric furnace used for extremely high temperaturesmelting of a ferroalloy according to claim 1, wherein said dual servicepipes are set up through the furnace lid as near electrodes as possible.

3. An improved electric furnace used forextremely high temperaturesmelting of a ferroalloy according to claim 1, wherein saidautomatically operated means comprises a reciprocating cleaningpiston'disc connected with a horizontal piston rod and an automaticdriving apparatus therefor.

4. An improved'electric smelting furnace according to claim 1 whereineach dual service pipe comprises'a lower chute portion having anupper-end that terminates within said forked position and saidautomatically operated means to remove dust comprises'a cylindricalrotary disc horizontally disposed on said upper end of said lower chuteportion, a vertical cleaning blade fixed to said rotary disc and drivemeans to rotate said rotary disc.

1. An improved electric smelting furnace of the closed-type whichcomprises a furnace lid, a plurality of single raw material chargingchutes having their discharge end extending through said lid, aplurality of dual service pipes extending at their discharge end throughsaid lid, each of said dual service pipes comprising a Raw materialcharging chute and an exhaust gas vent pipe, said chute and vent pipebeing joined at a forked position above said lid and automaticallyoperated means to remove dust from the junction of said chute and ventpipe at said forked position.
 2. An improved electric furnace used forextremely high temperature smelting of a ferroalloy according to claim1, wherein said dual service pipes are set up through the furnace lid asnear electrodes as possible.
 3. An improved electric furnace used forextremely high temperature smelting of a ferroalloy according to claim1, wherein said automatically operated means comprises a reciprocatingcleaning piston disc connected with a horizontal piston rod and anautomatic driving apparatus therefor.
 4. An improved electric smeltingfurnace according to claim 1 wherein each dual service pipe comprises alower chute portion having an upper end that terminates within saidforked position and said automatically operated means to remove dustcomprises a cylindrical rotary disc horizontally disposed on said upperend of said lower chute portion, a vertical cleaning blade fixed to saidrotary disc and drive means to rotate said rotary disc.